Journal of Biomolecular NMR, 23: 155–156, 2002. KLUWER/ESCOM © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 155 Letter to the Editor: Assignment of the 1 H, 13 C and 15 N resonances and secondary structure of the monomeric p13 suc1 protein of Saccharomyces pombe Benoît Odaert a,b,∗ , Isabelle Landrieu a , Klaas Dijkstra b , Gea Schuurman-Wolters b , Peter Casteels c , Jean-Michel Wieruszeski a , Ruud Scheek b & Guy Lippens a a CNRS UMR 8525, Institut de Biologie de Lille/Pasteur Institute of Lille, 59019 Lille Cedex, France; b The Gronin- gen Biomolecular Sciences and Biotechnology Institute, University of Groningen, 4 Nijenborgh, 9747 Groningen, The Netherlands; c Laboratorium voor Genetica, Department of Plant Genetics, Flanders Interuniversity Institute for Biotechnology (VIB), Universiteit Gent, K.L. Ledeganckstraat 35, B-9000 Gent, Belgium Received 30 January 2002; Accepted 20 March 2002 Key words: cell division, domain swapping, NMR spectroscopy, protein folding, p13 suc1 Biological context The cyclin dependent kinases (CDK) drive the pro- gression of the mitosis. In addition to the activating cyclin protein, the kinase complex contains a small subunit called CKS for cyclin-dependent kinase sub- unit (Brizuela et al., 1987). CKS proteins are essential for the entry and exit of mitosis and target the wee1 and CDC25 kinase regulators to phosphorylation by the CDKs (Patra et al., 1999). The CKS protein from Saccharomyces pombe, p13 suc1 , exists both in a closed conformation (Endicott et al., 1995) and in a C-terminal β-strand exchanged conformation (Bourne et al., 1995; Khazanovich et al., 1996). Mutation of the hinge proline P90 of p13 suc1 from S. pombe to alanine has been previously shown to stabilize the protein and to prevent swapping to occur (Rousseau et al., 1998). We have started NMR studies of the CKS protein from Saccharomyces pombe, p13 suc1 and the PA90 mutant. We have shown by NMR chemical shift perturbations that the p13 suc1 of S. pombe binds via its conserved anion-binding site to a CDC25 phosphatase peptide in a phosphorylation-dependent way (Landrieu, 2001; Odaert, 2002). We present here the backbone assign- ment of the wild type and the complete assignment for the PA90 mutant protein. ∗ To whom correspondence should be addressed. E-mail: B.J.E. Odaert@chem.rug.nl Methods and experiments Expression and purification were described previously (Odaert et al., 2002). [ 15 N] and [ 15 N, 13 C]-labeled wild-type and p13PA90 mutant proteins were ex- pressed in the minimal medium M9 supplemented by [ 15 N] ammonium chloride (1 g l -1 ) and [ 13 C] glucose (2 g l -1 ) (Cambridge Isotopes Laborato- ries, Cambridge, MA). NMR samples contained 1– 2 mM labeled protein in 100 mM NaCl 50 mM Na 2 HPO 4 /NaH 2 PO 4 (pH 6.8) in 5%:95% D 2 O/H 2 O or 100% D 2 O. NMR data were recorded at 20 ◦ C on a Bruker DMX600 (Pasteur Lille) and on a Varian Inova 600 (GBB) equipped with a triple-resonance 5 mm probe with a z gradient coil. Data were processed on an O2 workstation with the program SNARF v0.8.9 (Frans van Hoesel, University of Groningen). Backbone as- signment was achieved with the 3D triple resonance experiments (Sattler et al., 1999): HNCA/HN(CO)CA and HNCO/HN(CA)CO. Sidechain resonance assign- ment was achieved with the following experiments: HNCACB, CBCA(CO)NH, HBHA(CBCACO)NH, (CO)N(CO)CAH (Dijkstra et al., 1997), HCCH- TOCSY, 15 N-edited TOCSY-HSQC and 13 C-HSQC (aromatic region). The assignment was confirmed and completed with 15 N-edited NOESY-HSQC (100 ms mixing time) and 13 C-edited HSQC-NOESY (36 ms mixing time) in H 2 O and D 2 O.